Effect of thermal annealing on the properties of ZnO thin films

This work reports the effect of thermal annealing ranging from 0 to 800 °C on the various properties of zinc oxide thin film grown using radio-frequency sputtering. X-ray diffraction studies reveal the relaxation of stress up to thermal annealing of 400 °C and induction of residual stress thereafter. Zn K-edge X-ray absorption spectroscopic measurements reveal the variation of Zn–O and Zn–Zn bond distances with annealing temperature. Variation of coordination number with annealing temperature shows onset of oxygen vacancies at lower annealing temperatures. These vacancies and defects are also supported by the photoluminescence measurements. The optical band-gap of these films exhibit a significant variation with annealing temperature, which is in-line with the variation of crystallite size. Further, the magnetic behavior of these films is observed to follow the behavior of O 2p states along with defects as investigated from the X-ray magnetic circular dichroism.